The present invention relates to power MOSFET gate driver circuits. In particular, the present invention relates to the prevention of shoot-through currents in MOSFET switching circuits, for example, in half-bridge and H-bridge switching circuits for switching a load, for example, an electric motor. In a typical MOSFET switching circuit, for example a half-bridge circuit, there are two MOSFETs arranged in series, one of which is the high side switch and the other the low side switch. The high side switch is connected to a first higher voltage source and the low side switch may be connected to a second lower voltage source or ground. The two switches are operated alternately so that neither of the two switches is on at the same time. Often a dead time is arranged between the on times of the two switches to ensure that neither is on at the same time. A problem arises in that due to stray capacitances, the high side driver may inadvertently be turned on at the same time that the low side driver is on, thus creating a short circuit. When the high side switch is turned off, conventionally the gate and the source of the switch are connected by a low resistance path so that the gate and source will almost have the same voltage. If the difference between the gate and source is less than the threshold voltage VT of the FET, the FET will remain off. However, in some applications, for example H-bridge motor drivers, as shown for example in FIG. 1, when the source of the high side FET M1 is switched very quickly from the power supply voltage to ground by the switching action of low side switch M2, an electric charge may be injected into the gate of the high side switch M1 through the stray capacitances CDG1 and CGS1, the drain-gate and gate-source capacitances, particularly due to currents from inductive loads such as motors. This will increase the gate-source voltage of the high side switch M1 and if this voltage is higher than the threshold voltage VT of the high side switch M1, the high side switch M1 will turn on, causing a shoot-through short circuit between the power supply and ground and damaging the circuit, in particular, irreversibly damaging the FETs.
In the past, one solution to this problem has been to place a very low resistance path between the gate and the source during turn off, as mentioned above. However, this solution causes unnecessary current drains and thus wastes power and further may inhibit switching operation.